Malicious "jquery"

A social engineering trick that the people behind drive-by downloads are using is that of hiding their malicious code in the middle of benign, well-know code.

For example, recently, a number of compromised web sites have found their pages modified with iframes pointing at hxxp:// At a cursory inspection, jquery.js looks like the jQuery library, a well-known (and definitely benign) JavaScript library. The code includes the standard jQuery's copyright notice and revision information, and the first 6K bytes or so are indeed identical to the original library's code.

 * jQuery JavaScript Library v1.3.1
 * Copyright (c) 2009 John Resig
 * Dual licensed under the MIT and GPL licenses.
 * Date: 2009-01-21 20:42:16 -0500 (Wed, 21 Jan 2009)
 * Revision: 6158
(function(){var l=this,g,y=l.jQu...

However, the malicious code is hidden toward the end of the script, where one finds:

if( (typeof(jquery_data)!=typeof(1)) && 

This code determines whether an attack has already been launched, by checking the jquery_data variable and the miek cookie. If not, it deobfuscates a long string and writes it in the current page. The deobfuscated string creates a new script tag which points at hxxp:// The value of the id parameter in the script URL is 100 if the codename of the browser starts with the letter M (e.g., Firefox and Internet Explorer), 101 in all other cases. This page, in turn, attempts to launch a number of exploits (see the Wepawet report. The exploits target vulnerabilities in MDAC, PDF, and SWF.

It's certainly true: thing are not always what they seem...

  1. Polprav October 16, 2009

    Hello from Russia! Can I quote a post in your blog with the link to you?

  2. Marco October 19, 2009

    Sure, go ahead.

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